Windows File Server to NAS Migration Guide

Replacing an aging Windows file server with a NAS is one of the most common SMB IT projects. A suitable NAS can reduce power, licensing, and management costs for an SMB-only file-server workload, but the result depends on hardware, support, backup, retained Windows Server roles, and required Windows features. This guide covers migrating from a Windows Server (2016/2019/2022) to a Synology or QNAP NAS: inventorying existing shares and permissions, migrating data, recreating user accounts and share permissions on the NAS, and transitioning clients with minimal downtime. Both Synology DSM and QNAP QTS support AD domain membership and Windows-oriented SMB permissions, but they do not provide universal Windows Server feature parity; validate ACL, Offline Files, and DFS behavior for the selected NAS and software version.

Phase 1: Inventory the Existing Windows File Server

Before migrating, document what exists on the current server. Run the following on the Windows Server to export share and permission information:

net share > shares.txt
Get-SmbShare | Select-Object Name,Path,Description | Export-Csv shares.csv
Get-Acl -Path C:\Shares\* | Format-List | Out-File permissions.txt

Document for each share:

• Share name and UNC path (e.g. \\SERVER\Finance)
• Local path on server (e.g. D:\Shares\Finance)
• Users and groups with access, and their permission level (Read, Read/Write, Full Control)
• Approximate data size: Get-ChildItem -Path D:\Shares\ -Recurse | Measure-Object -Property Length -Sum

This inventory drives the NAS share structure and user account setup.

Phase 2: Set Up NAS Shares and User Accounts

On the NAS, recreate the share and user structure from your inventory:

Option A: Local NAS users (small workgroups without Active Directory):

1. Create a shared folder on the NAS for each Windows share (e.g. Finance, Projects)
2. Create user accounts matching your Windows Server user names (same username, new password. Distribute to users)
3. Assign each user to the appropriate shared folders with Read or Read/Write permissions in the NAS control panel

Option B: Active Directory domain join (workgroups with an AD domain):

1. On Synology: DSM → Control Panel → Domain/LDAP → Join domain. Enter domain controller details
2. On QNAP: QTS → Control Panel → Privilege → Domain Security → Active Directory authentication (Domain member) → Quick Configuration Wizard
3. After joining, AD users and groups are available in the NAS share permission editor
4. Assign AD groups to NAS shared folders. The NAS supports Windows-style share and file/folder permissions, but ACL semantics and limits can differ from Windows Server; pilot-test inheritance, explicit and deny entries, ownership, auditing information, and local SIDs.

AD domain join means users authenticate with their existing domain credentials. No new password distribution required. Strongly recommended if you already have an AD domain.

Phase 3: Migrate Data with Robocopy

Robocopy is the standard tool for migrating Windows file server data. Run from the Windows Server or a client with access to both source and destination:

robocopy "\\SERVER\Finance" "\\NAS-IP\Finance" /E /COPYALL /DCOPY:T /R:3 /W:5 /LOG:migration_finance.log /TEE

Key flags:

• /E. Copy all subdirectories including empty ones
• /COPYALL. Copy file data, attributes, timestamps, and Windows ACLs. Synology DSM and QNAP QTS can store Windows-style file and folder ACLs on supported volumes when the relevant Windows ACL features are enabled. Validate Robocopy ACL transfer, inheritance, local SIDs, ownership, and auditing data before migration.
• /DCOPY:T. Preserve directory timestamps
• /R:3 /W:5. 3 retries, with a 5-second wait between failed-copy attempts
• /LOG. Write log to file for audit trail

For large migrations: run an initial robocopy pass to copy the bulk of data (this can run overnight), For cutover, first disable writes to the source and then run a tested final delta or mirror pass. /XO only excludes source files older than the destination and does not remove destination items absent from the source; use /MIR only when its deletion behavior is intended and the paths have been verified. The second pass runs quickly and minimises the cutover window.

Phase 4: Client Cutover

Transitioning clients from the Windows Server to the NAS can be done two ways:

DNS redirect (zero-client-change): Do not treat a DNS change alone as an SMB cutover. Configure a vendor-supported NAS identity or SMB alias, reproduce the share names, register and verify the required CIFS SPNs for Kerberos, and test authentication before redirecting clients. Cleanest approach for large numbers of clients.

Group Policy mapped drives update: If clients have mapped drives assigned via Group Policy, update the GP drive mapping to point to the NAS UNC path. Push the GP update. Clients receive the new mapping at next logon or policy refresh.

Manual re-mapping (small environments): For 5-10 users, update each client's drive mappings manually. Right-click the mapped drive → Disconnect. Then Map Network Drive → enter the NAS path (\\NAS-IP\Finance). This takes 2-5 minutes per workstation.

After cutover, verify: users can read and write, permissions are correct for each group, and no users report access issues. Retain the old server temporarily as a controlled fallback, but remove normal user access and keep the source shares read-only after the final sync to prevent divergent copies.

Phase 5: Post-Migration Checklist

After the cutover:

• ✅ Verify all share permissions. Test with a standard user account (not admin)
• ✅ Confirm backup is running on the NAS (Hyper Backup or Hybrid Backup Sync)
• ✅ Update DNS records to reflect the new NAS as the file server
• ✅ Document the new share paths and share them with users
• ✅ Before granting users write access to the NAS, disable writes to the old shares and run the final verified Robocopy pass; retain the old data read-only afterward.
• ✅ Test restore from the NAS backup before decommissioning the Windows Server
• ✅ Decommission Windows Server or repurpose for other roles

🇦🇺 Australian Buyers: NAS Recommendations for SMB Migration

Recommended NAS for Windows file server replacement in Australian SMB environments (March 2026):

• Synology DS423+ (discontinued; DS425+ is the current model in this line): Most common SMB file server replacement. Active Backup for Business (agent-based Windows PC backup; agentless SMB file-server backup), strong AD integration, Hyper Backup for cloud offsite. Actual SMB workload capacity depends on file size and count, storage and RAID performance, network speed, encryption, concurrent activity, and other services running on the NAS.
• Synology DS925+ (~$1062): AMD Ryzen V1500B. Its suitability for heavier workloads depends on file-operation patterns, storage configuration, networking, memory, encryption, and other enabled services rather than a fixed user-count threshold. Same software suite
• QNAP TS-464 (~$989): Good alternative for environments that want hardware flexibility (PCIe 10GbE upgrade path). QTS Active Directory integration is mature. Hybrid Backup Sync handles cloud backup

For environments needing 10GbE for high-throughput file sharing (video production, large CAD files), consider Synology DS1823xs+ or QNAP TS-873A with a compatible optional PCIe 10GbE adapter, or add a PCIe 10GbE card to the TS-464.

See the small business NAS setup guide for a complete walkthrough of configuring a new NAS for SMB use, and the best NAS guide for broader model comparisons.